Conventional jet transport aircraft typically include retractable landing gears to reduce aerodynamic drag during flight. Such landing gears can extend downwardly from a wing or fuselage for landing and retract upwardly into corresponding gear wells for flight. Many aircraft also include at least some form of gear door that closes over the gear wells when the landing gears are in the extended position. When closed, these gear well doors can protect systems within the gear wells from foreign object damage during takeoff and landing, and can reduce noise and drag. Throughout the following disclosure, unless otherwise noted, the term “gear doors” refers to gear well doors that at least partially cover gear wells after extension of the corresponding landing gear.
When a conventional jet transport aircraft begins its takeoff roll, the gear doors are typically closed and remain in this position until after liftoff. Under current practice, pilots wait until the aircraft has achieved a positive rate of climb before initiating landing gear retraction. This usually occurs about three seconds after liftoff. Landing gear retraction typically begins with the opening of the gear doors to expose the gear wells. Next, the landing gears retract upwardly into the corresponding gear wells. When the landing gears are fully retracted, or close to fully retracted, the gear doors begin closing behind the landing gears to cover the gear wells for flight.
Retracting the landing gears quickly after liftoff can provide a number of benefits. One benefit is the reduction in aerodynamic drag and the corresponding increase in climb-rate that results from “cleaning up” the aircraft. Another benefit is the additional clearance that retracting the landing gear can provide between the aircraft and ground obstacles during an obstacle-limited takeoff.
Conventional jet transport aircraft typically have hydraulically driven landing gear systems. On such aircraft, the demands of the landing gear system typically determines the size of the hydraulic system. One known method for increasing the speed of landing gear retraction is to increase the capacity of the hydraulic system. One downside to this approach, however, is the increased cost associated with a larger hydraulic system. A further downside is the reduction in aircraft performance that results from the increased weight of a larger hydraulic system.